<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
    <script>
        var txt = "";
        function message() {
            try {
                adddlert("Welcome guest!");
            }
            catch (err) {
                txt = "本页有一个错误。\n\n";
                txt += "单击确定继续跳转\n";
                txt += "或者单击取消返回\n\n";
                if (confirm(txt)) {
                    document.location.href = "http://www.runoob.com/";
                }
            }
        }
    </script>
</head>

<body>
    <input type="button" value="查看消息" onclick="message()" />
</body>

</html>